1. Technical Field
The present invention relates to a laminate adhesive and, more particularly, to a laminate adhesive that is useful for the manufacture of packaging materials for use in a variety of industrial fields, including packaging materials for food products, beverages, medical products and quasi-drugs and to a usage thereof.
2. Description of the Prior Art
Composite films produced by laminating plastic films, metal foils, such as aluminum foils, metallized films and silica evaporated films by the application of an adhesive have been widely used as packaging materials for use in a variety of industrial fields, including packaging materials for food products, beverages, medical products and quasi-drugs, up to the present date.
The so-called two-component urethane adhesive, using a curing component containing polyisocyanate in combination with a base component containing polyol, such as polyester polyol, is used most as the laminate adhesive for use in the manufacture of these packaging materials, because of its excellent adhesion properties.
This two-component urethane adhesive is known, for example, from JP Patent Publication No. Sho 58(1983)-11912 which proposes that a silane coupling agent is mixed with the urethane adhesive in order to enhance an adhesive strength between the plastic film and the metal foil. Indeed, the mixing of the silane coupling agent with the base component is practically in wide use.
In recent years, from the aspect of hygienic importance, the sterilization treatment that the packaging products made from those composite films go through a high-temperature sterilization treatment, such as a hot-water spray sterilization treatment, a hot-water rotary sterilization treatment or a steam sterilization treatment is being widely carried out. After the high-temperature sterilization treatment, however, the composite film may have the problem that the plastic film and the metal foil of the composite film are delaminated.
It is conceivable that a quantity of silane coupling agent mixed is increased, in order to prevent this delamination, but the increase of the quantity of siliane coupling agent mixed may cause the problem that the odor and taste of the inherent properties of the content packed by the packaging product are spoiled.